The overall objective of this project is to further our understanding about the sources of outdoor air pollution that are detrimental to human health. Observational approaches to investigating effects of air pollution typically employ measurements of outdoor air pollutant concentrations obtained from one or more pollution monitors used to reflect pollutant exposures in a large urban area. Findings from studies that use ambient air pollutant concentrations to specify exposure are often difficult to interpret. An alternative approach is to attempt to measure effects associated with specific sources of air pollution. We propose to apportion sources of air pollution through detailed analyses of air pollution monitor filters and a factor analysis approach in order to address the following hypotheses: 1. A source-oriented approach will identify one or more ambient pollutant sources that contribute to short-term adverse health effects. Specifically, a source-oriented approach will identify an association between motor vehicle emissions and adverse health effects. 2. Use of a multivariate, "receptor-based" approach is a valid approach to identifying pollution source contributions to the ambient pollution mix in a large urban area. The primary hypothesis (1) will be tested by investigating the daily occurrence of several health outcomes in the Denver metropolitan region in relation to short-term changes in air pollution exposure specified by the source-oriented approach and the traditional approach using only air pollutant concentrations. The health outcomes to be studied include daily mortality, daily hospitalizations in the elderly with respiratory and cardiovascular diagnoses, daily emergency room visits to Denver area hospitals for selected respiratory and cardiovascular illnesses, and daily measures of asthma control in a sample of asthmatic school children. Attempts to control air pollution for the purpose of protecting public health are hampered by the limited information available on the sources of air pollution that are most harmful. Without this information, policies aimed at reducing concentrations of individual pollutants globally without focusing on specific sources will continue to be inefficient and less effective than they could be in protecting the population from the adverse effects of air pollution exposure.